Migration of leukocytes from blood vessels into diseased tissues is important to the initiation of normal disease-fighting inflammatory responses. But this process, known as leukocyte recruitment, is also involved in the onset and progression of debilitating and life-threatening inflammatory and autoimmune diseases. The pathology of these diseases results from the attack of the body's immune system defenses on normal tissues. Thus, blocking leukocyte recruitment to target tissues in inflammatory and autoimmune disease would be a highly effective therapeutic intervention. The leukocyte cell classes that participate in cellular immune responses include lymphocytes, monocytes, neutrophils, eosinophils and basophils. In many cases, lymphocytes are the leukocyte class that initiates, coordinates, and maintains chronic inflammatory responses, and thus are generally the most important class of cells to block from entering inflammatory sites. Lymphocytes attract monocytes to the site, which, collectively with lymphocytes, are responsible for such of the actual tissue damage that occcurs in inflammatory disease. Infiltration of lymphocytes and/or monocytes is responsible for a wide range of chronic, autoimmune diseases, and also organ transplant rejection. These diseases include, but are not limited to, rheumatoid arthritis, atherosclerosis, psoriasis, chronic contact dermatitis, inflammatory bowel disease, multiple sclerosis, sarcoidosis, idiopathic pulmonary fibrosis, dermatomyositis, skin pemphigoid and related diseases, (e.g., pemphigus vulgaris, p. foliacious, p. erythematosis), glomerulonephritides, vasculitides, hepatitis, diabetes, allograft rejection, and graft-versus-host disease.
This process by which leukocytes leave the bloodstream and accumulate at inflammatory sites, and initiate disease, is best understood for neutrophils and monocytes, but is likely to be similar for other lymphocytes. This process takes place in at least three distinct steps which have been described as (1) rolling, (2) activation/firm adhesion and (3) transendothelial migration [Springer, T. A., Nature 346:425-433 (1990); Lawrence and Springer, Cell 65:859-873 (1991); Butcher, E. C., Cell 67:1033-1036 (1991)]. The second step is mediated at a molecular level by chemoattractant receptors. Chemoattractant receptors on the surface of leukocytes bind chemoattractant cytokines secreted by cells at the site of damage or infection. Receptor binding activates leukocytes, and increases the adhesiveness of the adhesion molecules that mediate transendothelial migration.
A recent discovery is the existence of a large family (&gt;20 members) of structurally homologous chemoattractant cytokines, approximately 8 to 10 kD in size. These moleculles share the ability to stimulate directed cell migration (chemotaxis) and have been collectively called "chemokines", a contraction of chemotactic cytokines. All of these molecules contain four cysteine residues (C) and two internal disulfide bonds. Chemokines can be grouped into two subfamilies, based on whether the two amino terminal cysteine residues are immediately adjacent (C-C family) or separated by one amino acid (C-X-C family). These differences correlate with the organization of the two subfamilies into separate gene clusters. Within each gene cluster, the chemokines typically show sequence similarities between 25 to 60%.
The chemokines of the C-X-C subfamily, such as interleukin-8, are produced by a wide range of cell types and act predominantly on neutrophils as mediators of acute inflammation. Chemokines of the C-C subfamily are also produced by a wide variety of cell types. These molecules act predominantly on subsets of mononuclear inflammatory cells. Currently there are at least six C-C chemokines with known chemotactic activity for human monocytes and/or T cells, including MCP-1, MCP-2, MCP-3, MIP-1-.alpha., MIP-1.beta. and RANTES. This suggests there may be a high degree of redundancy in chemoattractant pathways. In addition, most C-C chemokines are chemotactic for more than one cell type. For examples, RANTES (regulated on activation, normal T cell expressed and secreted) acts on memory CD4.sup.+ T cells, eosinophils, and monocytes. Monocytes chemoattractant protein-1 (MCP-1), another C-C chemokine, acts on monocytes, activated "memory" T cells and on basophils. MCP-1 is a potent secretogogue.
Five C-C chemokine receptors have recently been characterized (CKR1-5), and all of these belong to the seven transmembrane spanning G protein-coupled receptor family. Each of these receptors indicates the binding and signalling of more than one chemokine. For example, the CKR1 receptor binds both MIP-1.alpha. and RANTES. There are 2 receptors which bind MCP-1, CKR2 (with alternately spliced forms, 2A and 2B) and CKR4. CKR2 is also known to mediate binding and signaling of MCP-3. The CKR4 receptor binds and signals, in addition to MCP-1, with RANTES and MIP-1a. Which of these is responsible for the MCP-1 mediated recruitment of monocytes and T cells is not known.
In agreement with the observation that lymphocyte emigration into inflammatory sites is usually accompanied by emigration of monocytes, MCP-1 is expressed at sites of antigen challenge and autoimmune disease. However, analyses of human inflammatory lesions with antibodies to other chemokines show RANTES, MIP-1.alpha., MIP-1.beta. and MCP-3 to be present as well. Injection of MCP-1 into skin sites in mice provokes only a mild monocyteic infiltrate or no infiltrate at all (Ernst, C. A. et al., J. Immunol. 152:3541-3544, 1994). Whether these results reflect redundant and complex recruitment pathways has not been resolved. MCP-1 and MCP-3 may play a role in allergic hypersensitivity disease. This is also suggested by the observation that MCP-1 lacking the amino terminal glutamic acid loses the ability to stimulate basophil mediator release and acquires activity as an eosinophil chemoattractant.
Chemokines of both subfamilies may bind to heparan sulfate proteoglycans on the endothelial cell surface, and may function principally to stimulate haptotaxis of leukocytes that attach to cytokine-activated endothelium through induced adhesion molecules. Additionally, the MCP-1 chemokine appears to selectively activate the .beta.1 integrin family of leukocyte adhesion molecule, suggesting a role in leukocyte interactions with the extra cellular matrix rather than with the endothelium. Hence, MCP-1 may not only trigger the initial arrest and adhesion of monocytes and T cells, but may rather act to guide their migration in extravascular space.
Chemoattractants appear to be required for transendothelial migration in vitro and in vivo and can induce all steps required for transmigration in vivo. Injection of neutrophil chemoattractants into skin or muscle leads to robust emigration of neutrophils from the vasculature and accumulation at the injection site (Colditz, 1991). Pretreatment of neutrophils with pertussis toxin inhibits emigration into inflammatory sites (Spangrude, et al., 1985; Nourshargh and Williams, 1990). Moreover, MAb to IL-8 markedly inhibits neutrophil emigration in inflammation (Sekido et al., 1993).
Neutrophil chemoattractants injected into the same skin site hours apart will stimulate neutrophil accumulation the first time but not the second time, whereas a second injection into a distant site will stimulate accumulation at that site. This desensitization occurs for homologous chemoattractants only (Colditz, 1991) or those that interact with the same receptor. Thus, chemoattractants can act on and homologously desensitize a cell type that is localized in tissue.
Chemoattractants impart directionality to leukocyte migration. By contrast with intradermal injection, intravascular injection of IL-8 does not lead to emigration (Hechtman et al., 1991). Cytokine-stimulated endothelial monolayers grown on filters secrete IL-8 into the underlying collagen layer. Neutrophils added to the apical compartment emigrate into the basilar compartment, but not when the IL-8 gradient is disrupted by addition of IL-8 to the apical compartment (Huber et al., 1991).
The endothelium may present chemoattractants to leukocytes in a functionally relevant way, as well as providing a permeability barrier that stabilizes the chemoattractant gradient. Since leukocytes, responding to specific antigen or inflammatory signals in tissue, may signal emigration of further leukocytes into the site, a chemoattractant was sought in material secreted by mitogen-stimulated mononuclear cells (Carr et al. 1994). Purification to homogeneity guided by a transendothelial lymphocyte chemotaxis assay revealed that monocyte chemoattractant protein 1 (MCP-1), previously thought to be solely a monocyte chemoattractant, is a major lymphocyte chemoattractant. An activated subset of memory lymphocytes respond to MCP-1. In the same assay, lymphocytes respond to RANTES and MIP-1.alpha. but less so than to MCP-1 (C-C chemokines) and not at all to IL-8 or IP-10 (C-X-C chemokines). This physiologically relevant assay suggests that C-C chemokines tend to attract both monocytes and lymphocytes. In agreement with the observation that lymphocyte emigration into inflammatory sites is accompanied by emigration of monocytes, MCP-1 is abundantly expressed at sites of antigen challenge and autoimmune disease (Miller and Kragel, 1992) and, together with other chemokines, is an excellent candidate to provide the step 2 signal required to activate integrin adhesiveness and emigration of lymphocytes in vivo. Traffic Signals for Lymphocyte Recirculation and Leukocyte Emigration: The Multistep Paradigm; Springer, 1994, Cell 76: 301-314).
We have surprisingly found that pyrazolone derivates are MCP-1 receptor antagonists (inhibiting the binding of MCP-1 to its receptor). Surprisingly, the compounds block T cell migration in vitro, and more surprisingly still, have dramatic effects on the recruitment of inflammatory cells in multiple models of inflammatory diseases. Thus, these compounds are useful as agents for the treatment of inflammatory disease, especially those associated with lymphocyte or monocyte accumulation or recruitment, such as arthritis, atherosclerosis and transplant rejection. In addition, these compounds can be used in the treatment of allergic hypersensitivity disorders such as asthma and allergic rhinitis characterized by basophil activation and eosinophil recruitment, as well as for the treatment of restenosis and chronic or acute immune disorders.